Open-window noise canceling system cuts outside sounds

Researchers at Nanyang Technological University (Singapore) have developed a window-mounted system that can reduce noise pollution entering buildings even while windows are wide open.

Designed to be mounted onto window grilles, the system uses active noise control technology – similar to that found in noise-canceling headphones that cancel external noise – adapted to work in a large open area. According to the researchers, their technology could reduce up to 50% of the noise coming from the nearby environment, such as that caused by busy roads, trains, or construction, allowing building occupants to experience fresh air without disturbance as well as reducing the need for air conditioning.

"Compared to noise cancellation headphones," says Professor Gan Woon Seng, Director for NTU's Center for Infocomm Technology, who led the research, "what we have achieved is far more technically challenging as we needed to control the noise in a large open area, instead of just around the ear."

The prototype unit uses eight watts of power - similar to that of a small portable Bluetooth speaker - and uses a special sound-emitting mechanism that works like a speaker and is hooked up to a processing unit. To set up the system, several such units with associated small microphones are placed together in a grid-like array on a window grille.

In operation, the system detects noise even before it reaches the window and computes the characteristics of the incoming noise in real time. It then emits a countering sound or "anti-noise" that has the opposite - or inverted - waveform characteristics of the invading noise. When the two sounds converge, they cancel each other out, resulting in a quieter ambient sound entering the living space.

"Our innovation not only computes the right amount and type of "anti-noise" to emit," says Gan, "but also does it faster than the detected noise can reach inside the building."

The researchers conducted their tests using a soundproof chamber at the university's labs that houses a faux room with windows and doors - resembling a typical room in a home. They used various recorded